Problem: $ { \left[\begin{array}{rr}{2} & {1} \\ {2} & {1}\end{array}\right]+\left[\begin{array}{rr}{1} & {-1} \\ {0} & {1}\end{array}\right] = {?} } $
To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{2}+{1} & {1}+{-1} \\ {2}+{0} & {1}+{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{3} & {0} \\ {2} & {2}\end{array}\right]}$